1. Field of the Invention
This invention relates to organic polyisocyanates and is more particularly concerned with modified organic polyisocyanates obtained from carbodiimide-containing polyisocyanates and to the glassy polyurethanes obtained from said modified polyisocyanates.
2. Description of the Prior Art
Carbodiimide-containing organic polyisocyanates derived from different types of organic polyisocyanates are well known in the art having been prepared by a variety of methods; see for example U.S. Pat. Nos. 3,384,653, 3,761,502, and 4,143,063, and German Patent Application DT No. 25 04 400. Generally speaking, the primary purpose for introducing the carbodiimide linkages into the organic polyisocyanates in the first place is to ensure that they remain in a liquified and fluid state when stored for extended periods of time even at reduced temperatures.
Carbodiimide-containing polyisocyanates, for the most part, tend to be insoluble in organic solvents. U.S. Pat. No. 4,077,989 discloses a method whereby such polyisocyanates are solubilized by converting some or all of the carbodiimide groups into acylated urea groups by reacting the carbodiimide-containing polyisocyanate with certain mono- or polycarboxylic acid compounds.
We have now discovered that carbodiimide-containing polyisocyanates can be modified by the formation of adducts with certain carboxylic acid terminated butadiene-acrylonitrile copolymers to give rise to novel and useful liquid polyisocyanate compositions.
When the isocyanate compositions in accordance with the present invention are used in the preparation of solid glassy polyurethanes, the products so obtained are characterized by improved impact strengths with retention of good high temperature resistance properties.
A comparison of the impact strengths and heatdeflection temperatures of solid glassy polyurethanes prepared with polyisocyanates modified according to the teaching of U.S. Pat. No. 4,077,989, cited supra, with a solid glassy polyurethane prepared with a polyisocyanate in accordance with the present invention shows clearly the superior properties of the latter material (see Example 4 below).
Surprisingly, the impact strength improvement is greater than one would predict from the use of the carboxylic acid terminated butadiene-acrylonitrile copolymer as a reaction component directly in the urethane forming reaction mixture (see the comparison of plaque E with plaque F in Example 1 below); for a summary of the use of butadiene-acrylonitrile polymers in toughening plastics see "Toughening Thermosets with Liquid Butadiene/Acrylonitrile Polymers" by E. H. Rowe et al., Modern Plastics, 1970, 47, 110.
Aside from the novel and useful feature of carrying their own built-in impact improving agent, the isocyanates of the invention enjoy the other advantageous features attributed to the prior art carbodiimide-containing polyisocyanates.